You are here: Lean Six Sigma Home » Queueing Theory » queueing theory: part 1

queueing theory: part 1

by Pete Abilla on May 19, 2006

Interested in a free 25+ eBook on the 7 Wastes? Please DOWNLOAD HERE.

This post is part of a series on Queueing Theory. The other articles can be found here:

A queueing system is a model with the following structure: customers arrive and join a queue to wait for service given by n servers. after receiving service, the customer exits the system. a fundamental result of queueing theory is little’s law.

theorem: for a queueing system in steady state, the average length of the queue is equivalent to the average arrival rate multiplied by the average waiting time. in other words,

L = λW

at amazon, i used little’s law all the time. in dynamic systems with n+ dependencies, it is very helpful to know where the bottlenecks of the system are and how to increase efficiencies, reduce time traps, and eliminate waste in order to increase material flow. in other words, we want product to flow as fast as possible: click-to-ship.

here’s an example:

say there’s a warehouse with 4000 pallets of product that turns ~4 times per year. do we have enough labor to support these transactions? using little’s law, we get

4,000 = λ(.25year)

queueing theory computer applications, operations research, optimization, modeling, econometrics

so,

λ = 16,000 pallets/year

assuming a 10 hour shift per day of about 250 working days per year, there is roughly 2,000 working hours. this means, then,

λ = 8 pallets/hour

the analysis above is critically important to estimate the labor force required to move pallets, receive product, move product, and get work done, in general.

there are many more applications of queueing theory that i will explicate and share in the next while. queueing theory is a critical, underused, but very valuable principle in business.




search terms for this article:

application of queuing theory in business, Queueing Theory Utilization, capacity utilization queueing theory, theory of capacity utilization, application of queueing theory in business, throughput queueing theory, steady state queueing theory, steady state queuing theory, cycle time analysis using queueing theory, throughput queuing theory, queue theory throughput, how queuing theory works, queeing theory, little\s law in queuing theory, steady state in queuing theory, steady state in queing theory, steady state analysis queueing models, little\s law utilization, queueing theory steady state, queuing theory graphs, queue theory warehouse, queuing theory in management, queuing theory of unemployment, queuing theory service time, queue capacity queueing theory, queuing theory steady state, queuing theory capacity utilization, steadystate analysis in queuing models, application of queuing theory in business management, Fundamental of Queueing Theory, capacity utilization Vs cycle time, queuing theory in employment, QUEUING THEORY IN FACTORIES, what is busy period in queing theory, what is a steady state of a queue in queing theory, warehouse modeling game, queuing theory model 4, queuing theory on work, warehouse capacity utilization graph, utilization-queueing theory, queuing models in services, queuing theory explosive state, queing theory queing models estimating model parmeters throughput utilization, queuing models introduction, queuing models steady state, what is steady state in queueing theory, queuing models steady state analysis, What is queuing theory? How has queuing theory affected you?, queuing models utilization, queuing models utilization >1, queuing theory agile capacity, queuing theory and little\s result, queuing theory capacity management, utilization queuing theory normal, utilization little law, queuing theory steady state analysis, steady state in queuing model, work queuing theory, throughput queueing, steady state queuing model, steady state queuing models, throughput in queuing theory, steady state queuing theory 100% utilization, steady state result in queuing theory, throughput and utilization in queues, theory about time utilization, throughput rate queueing models, steady state analysis-queueing models, steady state analysis queueing theory, queuing theory wait time graph, queuing throughput analysis theory examples, steady state theory based on queuing theory, sample throughput graph of a steady state system, using queuing theory in business, use of queing theory in business, ship queuing models, steady flow queue theory, steady state analysis in queuing theory, time series queueing theory, theories time utilization, queuing analysis employment, 4 queuing models, explosive state on queuing theory, fundamental of queueing theory answer, fundamental of queueing theory 解答, fundamental of queueing theory solutions, game theory queue theory or theory, how is throughput time related to capacity and utilization, how queing theory works, how to determine the utilization rate in the queueing models, how to find throughput for queuing models, how to implement queuing in FMCG warehouse, Increasing Capacity Managing Demand in queueing theory, indroduction about little\s law, introduction about queueing theory, explosive state in queuing theory, explosive state in queuing system, explosive state in queueing theory, agile queuing theory, airplane queueing

Related Articles:


This post was written by

{ 8 comments… read them below or add one }

www.comp-nerds.co.nr May 20, 2006 at 3:37 pm

If you found this article interesting, please digg it at: http://digg.com/technology/queueing_theory so more people will find it.

Reply

Mark Graban June 15, 2006 at 7:51 am

Little’s Law is an incredbly helpful tool for operations. I highly recommend the Hopp and Spearman book “Factory Physics”, which spends a lot of time on Little’s Law.

Another way of thinking about this is:

Throughput = WIP / CT

WIP = Work in Process

You have to be careful with Little’s Law and resist the temptation to think “all I have to do to increase Throughput is to increase WIP”. It doesn’t work that way, not that Peter was implying that. I’m just saying that’s a common mis-application of Little’s Law.

When you start with zero WIP, you will have zero throughput. Makes sense, right? At first, as WIP increases, your throughput will increase somewhat linearly. But, as capacity utilization reaches 80% or so, throughput levels out and Cycle Time explodes. That’s why really busy systems (factories, emergency rooms, etc.) have very long waiting times. The Cycle Time explosion is made worse with variation. The more variation you have in customer demand and service time, the worse the Cycle Time explosion is. That’s why leveling (heijunka) is key…. on to Peter’s second post, I’m looking forward to reading it.

This Industrial Engineer is just happy to see anyone discussing Little’s Law.

Reply

Mark Graban June 15, 2006 at 7:53 am

One problem with your analysis there is that you’re assuming demand (and labor needs) are constant throughout the year. I’m certain that wouldn’t be the case for Amazon or any retailer.

Reply

Richard Karpinski November 23, 2007 at 11:48 am

“assuming a 10 hour shift per day of about 250 working days per year, there is roughly 2,000 working hours.”

This works only if the 10 is in octal notation.

Reply

LT July 21, 2011 at 11:11 pm

10-hour shift, but 8-hour working. Hey, this is normal.

Reply

Bob Dierks January 12, 2009 at 10:48 pm

Refreshing!

Reply

Baruch Atta January 28, 2009 at 7:54 am

“…as capacity utilization reaches 80% or so, throughput levels out and Cycle Time explodes. That’s why really busy systems (factories, emergency rooms, etc.) have very long waiting times…”

No, that’s not the reason. The reason that ERs, restaraunts, and Post Offices have long wait times is that utilization (or demand) has gone over 100% throughput capacity. The service can no longer serve in the rate as people arrive. Since the service provider has not planned for or reacted to the higher demand, the length of the line grows.

Reply

Baruch Atta January 28, 2009 at 7:58 am

should read…
…can no longer serve at the rate that people arrive…

Reply

Leave a Comment